This invention relates to shaft couplings, and more particularly to improvements in couplings of the type which utilizes a grid which includes metal rungs joining the coupling halves.
A common form of flexible coupling used for joining driving and driven shafts employs a metal grid to join coupling halves mounted on the shafts being coupled. The grid is usually in the form of a serpentine with straight grid rungs joined together at alternate ends by integral end loops. The rungs are received in radially aligned, axially extending slots formed between teeth on each of the coupling hubs and the rungs span the space between the coupling halves. The rungs act as beams and the side walls of the teeth are generally curved in an axial direction so that as the torsional load transmitted between the coupling halves increases the unsupported length of each rung is reduced. An example of this type of flexible coupling is found in U.S. Pat. No. 1,763,842, issued June 17, 1930 to Bibby.
Another form of grid utilizes a series of closed loops each of which have a pair of straight rung portions joined at their opposite ends by loops. An example of such a coupling is found in U.S. Pat. No. 3,196,635, issued July 27, 1965 to Schmitter. Still another form of grid uses alternate U-shaped spring grid elements (see U.S. Pat. No. 2,555,909, issued June 5, 1951 to Wellauer).
In the flexible grid coupling the slots can have parallel sides with the rung portions of the grid having complimentary rectangular cross-sections. Alternatively, the sides of the slots may taper outwardly and the cross-section of the grid rungs may have a mating taper, as shown for example in U.S. Pat. No. 3,079,773, issued Mar. 5, 1963 to Schmitter.
In the prior flexible grid couplings, the grids are typically made of a metal, usually steel, which is heat treated to harden the grid and provide it with sufficient strength and resistence to fatigue because of the continual reversal of loads to which it is subjected. Heretofore, the grids have first been formed into shape and then heat treated to harden the grid. The heat treatment to harden the grid could not precede bending or forming because it would have been impracticable if not impossible to bend the hardened grid stock. Furthermore, the heat treating is needed to relieve stresses which are built up during the forming of the grid. The particular process used involved first bending the grid and then inserting it in a fixture to hold it during the heat treatment process. Inaccuracy in the grid results from the forming of the grid by reason of inaccuracies in machine set-up and worn dies, and also from the heat treatment which distorts the form of the grid. As a result, the formed and heat treated grid will not seat properly in the slots so that the rungs will be forced to carry unequal loads and stresses will tend to concentrate.
My invention employs a flexible grid which includes a series of straight metal rungs held at each of their ends in an elastomer member. The straight lengths forming the rungs can be heat treated to harden the grids before being cut into lengths and bonded to the elastomer members. The elastomer members provide a mechanism for holding the rungs during assembly, will accommodate misalignment between the couplings halves, and will not themselves impose loads upon the rungs.